sunflower 1972

Finished installing E-Tec Cylinder Heads in my 72. Engine temp gauge is reading 15 to 20 degrees hotter than the cast iron heads. Iron temps were 195*- 215*. Aluminum is 215* to 235*. Obviously, with brand new aluminum heads I had to use a brand new GM temp sending unit.
Doing a search of the forum, the general consensus seems to be the problem is the new temp sender. Everything that I heard about aluminum heads is the engine should run a little cooler with them. Just wondering if anyone else encountered the same issue when replacing cast iron heads with aluminum, and if the gauge temps seemed to be a showing a consistent 15* to 20* hotter?

Luce

I'll take a stab at some theory...

The aluminum heads keep the combustion chamber cooler by conducting the heat from the top of the chamber to the water better than cast iron. Odd thing chevy does is sense the temp for the gauge from the head deck rather than the water at the thermostat like ford and mopar. That's why the indicated temp is higher. My Cobra NEVER exceeds 200 (195 T stat) unless you kill it, then check it 2 minutes later.

Also, the sender is between exhaust ports, again, better heat transmission than iron getting the heat from the port to the sender.

I'm a bit new to GM. Grew up Mopar, then held my nose and built a Cobra. Other than wife's vette, the only GM I've had was a 2.8 S-10 blazer I got for near free, and only took it be cause I didn't have money and needed a ride.

hugie82

Variation in new sensor compared to the old one could be a 5-10 degrees off. Location on the head and material as stated above all have an effect. A cheap harbor freight temp lazer will tell the truth. Check each exhaust port making sure they're even and then hit the thermostat housing to get your true engine temp.

SwampeastMike

Sorry but a "cheap harbor frieght temp laser" (or an expensive one for that matter) won't really tell the truth. Such can only measure the temperature of the surface it sees--that means it won't measure the temperature of the coolant. You cannot assume that the two are the same temperature! Also the nature of the surface (especially its level of gloss) will affect the sensed temperature--this discrepancy between actual and sensed temperature can be extreme.

Cool95vette

The motors in my two cars are built pretty much identical with the same water pumps, radiators, fans, and thermostat. The only difference is the heads. One has iron and one has aluminum heads. The one with the aluminum heads runs about ten degrees cooler.

sunflower 1972

That's what I thought. Now, I just need to get the water temp sending unit thing sorted out. Luckily, I still have the original sending unit in the cast iron heads that I removed. Going to try that this weekend.

Silvertone

What kind of headers? Did you match up the exhaust ports to the headers? I've seen some 1 5/8" header openings that were actually smaller than the exhaust port on the head, causing a heat reversion which did not exist with the smaller iron head ports.

mikem350

To the OP...what temp sensor do you have that fits the head? Aftermarket heads normally have a smaller hole for the sensor. OEM fits in the intake water port.

sunflower 1972

GM part# 12334869. Thread size 1/2 x 14 NPT.Edelbrock 5089 alum heads.

sunflower 1972

Well, temp gauge doesn't read hotter anymore. Want to know what fixed it? I put the old, original 45 year old temp sending unit back in. See, sometimes older is better!

jb78L-82

I reused the OEM temp sender on my AFR Aluminum heads (had to have the AFR heads tapped for the OEM sender size precisely due to the variability with some of the new sending units) versus the OEM GM 882 cast iron heads and the temp stayed exactly the same...180 degrees on the button. The thermostat keeps the temp at a steady state as long as everything else in the cooling system is up to snuff. I had the L-82 355 out today and beat on it pretty well and the temp never moved from 180 degrees...AFR Aluminum heads, Robertshaw 180 thermostat, aluminum Dewitts radiator, aluminum Stewart Stage 2 water pump....tons of weight savings too....